This section investigates functional properties of excitatory amino acid receptors in the vertebrate CNS, utilizing electrophysiological and molecular biological techniques. Fast perfusion systems are used for concentration jump application of glutamate receptor selective agonists and antagonists to cells and membrane patches under voltage clamp. Preparations in use include primary cultures of hippocampal neurons and glial cells, and recombinant receptors expressed in transfected cells and oocytes. For NMDA receptors we have used agonist trapping during open channel block by 9-AA as a novel approach to estimate maximum open probability. Analysis of the molecular basis of AMPA receptor modulation by cyclothiazide is being investigated based on our observation that alternative splicing of the flip and flop variants, generated by use of alternative exons encoding 37 highly conserved amino acids, but which differ in core regions of only 4 + 1 amino acids, generates receptors with high and low sensitivity to cyclothiazide. Assay of cyclothiazide action on recombinant receptors, in which theses core residues are being exchanged, is being used to determine critical sites for allosteric modulation.